4.0L Ford Ranger CEL Codes. I need your opinion before I dive in.

[AceTrainerAndy]

Hello All,

I am a owner of a 2002 Ford Ranger 4.0L XLT. She has 210,000 miles. I used to own an Explorer and this forum was very great in helping me with it. I know you guys know a lot about 4.0L V6s.

Anyways, last Friday my truck was having acceleration issues. I would hit the gas and the RPMs shoot up but the acceleration was pitiful. My first thought was the notorious crappy transmissions in these things but the truck sounded like it had a bad exhaust leak . The best way to describe it is like a RAM with an exhaust leak. You'd know it if you heard it. This happened when I would do a cold start, but when the engine got warm it would do it under wide open throttle.

So the truck did this in July too. I took it to a shop and she got all new wires, ignition coils, and spark plugs. That fixed the problem. The mechanic did tell me my catalytic converters might be going bad from that.

I took it to the same shop this week and the guy said he diagnoses it as bad catalytic converters. He very low key recommended I cut them off and just straight pipe it. I did that yesterday, but I could only cut off three of the four. I couldn't cut off the bank 2 upstream cat. So to reiterate, I cut off the two big ones in the rear and the bank 1 up stream (little one close to exhaust manifold). This did not fix my problem. He said if you do that then you should try the O2 sensors. That's what I'm on now.

I have a dilemma though. I wasn't able to cut off the bank 2 upstream cat, so I can't completely rule the catalytic converters out. If you look down below you can see my codes are indicating bank 1 is where the problem is. I think it is a bad O2 sensor, but I can't afford to waste time and money on guessing.

Also please check my reasoning. As I understand it bank 1 of the engine is on the driver side of the vehicle. Is this right?

The CEL turned off, but I think that's because we disconnected the battery. Before I had an OBD reading. it threw the following codes

P0171 System Too Lean (Bank 1)
P0135 O2 Heater Circuit (Bank 1, Sensor 1)
P01131 Lack of HO2S11 Switches Sensor indicates lean
P0303 Cylinder 3 Misfire Detected

For me personally, that appears to be a bad up steam bank 1 O2 sensor. What do y'all think? I am just confused how a bad O2 could cause lean problems. My MAF looked good when I looked. I have looked at the fuel system yet, that could be it.

Thank you for your time! I appreciate it more than you could ever know!

 

[Turdle]

Looking for dots to connect in this puzzle leads me to this

A bad 02 sensor could be reporting bad data also. ( lean condition)

however, on the other hand, a bad fuel injector would also cause a misfire on cylider 3 ( p303) , and since cylinder 3 is on bank one it may also throw a lean condition code if that injector were to be clogged. ( low fuel too much air is lean)

Also check though the pcv valve and hoses because if they are leaking they will allow excess air to the passenger side of engine, and also could be the misfire source. I think this is where I would start and work back to the injector.

 

[AceTrainerAndy]

Hello All,

I wanted to post an update for future generations about this. Good news, my truck is fixed.

Ok, so that weekend my brother and I looked for vacuum leaks in the truck. I found one. The hose that connected my PCV to the main large intake came disconnected (apparently common 4.0 problem). This slightly helped my problem but the truck was still badly misbehaving by chugging under a heavy load.

The next weekend I found a shady muffler shop who completely redid my exhaust and cut off the last catalytic converter. I know it's illegal, but I let them keep the cat so it was probably worth it for them. So now, the truck was very quiet and has a sexy purr but she was still misbehaving. I couldn't believe it. The problem was slightly better but still noticeably there.

The next weekend my brother and I decided to tackle the dreaded O2 sensors. Also, by the way, I looked at the service manual and bank 1 is actually on the passenger side of the vehicle! I was wrong in the original post. I scrapped my knuckles replacing the O2 sensor on bank 1 and tried out the truck and it didn't work. We couldn't get the bank 2 sensor off. Our hands are too big to fit in that harness because the transmission shifter link is in the way and I was too scared to take it off. I was convinced it was a fuel delivery issue now and I was running out of patience.

I took it to my local shop and the guys there are so awesome. If you're in SE Michigan I highly recommend Winner's Auto! They were the original shop that diagnosed me as a bad cat or an O2 sensor. I walk in and tell the mechanic that I cut off the cats and replaced the O2 sensor that I thought was bad. The mechanic immediately told me that he thinks I either have a clogged valve or a fouled spark plug. He said pray it's a fouled spark plug or else the valve would require large labor costs because he would have to take off the head. I was just going to try seafoam if that was the case. The next day he calls me and says I have two fouled spark plugs and he had parts laying around so he replaced them for free. My truck runs like a dream and is getting better than the EPA est MPG at 211,000 miles! I am getting 21 MPG mainly highway.

So now that the mystery is solved I understand how this happened. Last June, my ignition coil went out and gave me a bad misfire. I didn't think much of it and I drove with a bad ignition coil for about a month (I didn't know it was the ignition coil at the time, I thought it might be O2 sensor). This clogged the hell out of my catalytic converter. I know I'm stupid for doing that. Please learn from my mistake. From now on, I will service my vehicles immediately instead of hoping it will go away. When you have a clogged catalytic converter this causes exhaust to get backed up and linger in places it's not supposed to like near the valves and spark plugs. I drove with a clogged catalytic converter for about 10 months and 15,000 miles before the spark plugs got so fouled they just couldn't continue under load. Please learn from my mistake and service vehicles immediately especially if CEL is blinking!